TY - JOUR
T1 - Timing of eclogite facies metamorphism in the southernmost Scandinavian Caledonides by Lu–Hf and Sm–Nd geochronology
AU - Smit, Matthijs Arjen
AU - Scherer, Erik
AU - Bröcker, Michael
AU - van Roermund, Herman
PY - 2010
Y1 - 2010
N2 - The Scandinavian Caledonides contain several non-cogenetic eclogite-bearing terranes that were metamorphosed before the main orogenic stage in Scandian time (430-395 Ma). Although petrological and geochronological data from these terranes have provided essential information on the geodynamic history of the Caledonian orogenic cycle, the general picture is still patchy. To refine existing geodynamic models, we have dated the eclogite occurrence in the Jæren nappe, SW Norway, by Lu-Hf and Sm-Nd geochronology. Five out of the six studied samples provide a weighted mean Lu-Hf age of 469.9 ± 1.2 Ma (±2σ). One sample provided a significantly younger age of 457.9 ± 2.4 Ma. Garnet from the younger sample grew exclusively at eclogite facies conditions. In contrast, garnet from the other samples comprises prograde cores and peak metamorphic rims. Age estimates that take Lu-contributions of each zone into account provide an age of 471.0 ± 0.9 Ma for the cores and suggest a ca. 455 Ma age for the rims, which is identical to the bulk-garnet age of the younger sample. The same pattern is indicated by Sm-Nd ages, although these are relatively imprecise and reflect isotopic disturbance during thermal overprinting upon exhumation. The data define a new high-pressure age population for the Scandinavian Caledonides, which allows more detailed insight into the subduction history that affected the Baltoscandian margin before Scandian continental collision. Furthermore, this study highlights the potential complexities involved in garnet geochronology and shows the strength of Lu-Hf dating for unraveling the geochronological record of HP rocks.
AB - The Scandinavian Caledonides contain several non-cogenetic eclogite-bearing terranes that were metamorphosed before the main orogenic stage in Scandian time (430-395 Ma). Although petrological and geochronological data from these terranes have provided essential information on the geodynamic history of the Caledonian orogenic cycle, the general picture is still patchy. To refine existing geodynamic models, we have dated the eclogite occurrence in the Jæren nappe, SW Norway, by Lu-Hf and Sm-Nd geochronology. Five out of the six studied samples provide a weighted mean Lu-Hf age of 469.9 ± 1.2 Ma (±2σ). One sample provided a significantly younger age of 457.9 ± 2.4 Ma. Garnet from the younger sample grew exclusively at eclogite facies conditions. In contrast, garnet from the other samples comprises prograde cores and peak metamorphic rims. Age estimates that take Lu-contributions of each zone into account provide an age of 471.0 ± 0.9 Ma for the cores and suggest a ca. 455 Ma age for the rims, which is identical to the bulk-garnet age of the younger sample. The same pattern is indicated by Sm-Nd ages, although these are relatively imprecise and reflect isotopic disturbance during thermal overprinting upon exhumation. The data define a new high-pressure age population for the Scandinavian Caledonides, which allows more detailed insight into the subduction history that affected the Baltoscandian margin before Scandian continental collision. Furthermore, this study highlights the potential complexities involved in garnet geochronology and shows the strength of Lu-Hf dating for unraveling the geochronological record of HP rocks.
U2 - 10.1007/s00410-009-0440-3
DO - 10.1007/s00410-009-0440-3
M3 - Journal article
SN - 0010-7999
VL - 159
SP - 521
EP - 539
JO - Contributions to Mineralogy and Petrology
JF - Contributions to Mineralogy and Petrology
IS - 4
ER -